Hybrid poplar (<Emphasis Type="Italic">Populus</Emphasis> ssp.) selections for arid and semi-arid intermountain regions of the western United States

The rapid growth rates of hybrid poplar (Populus spp.) enable rotations of 3–6 years for biofuels or 10–15 years to obtain merchantable timber, but many clones are susceptible to nutrient deficiencies when grown in alkaline soils. A 1995 Oregon study demonstrated that clone OP-367 (P. deltoides × P. nigra) was the only clone tested that performed well on alkaline soils. Tests in Colorado and New Mexico confirmed the adaptation of this clone. A multi-clonal trial was established in 2003 at Farmington, New Mexico and Ontario, Oregon in order to screen a larger number of clones for adaptability to alkaline soils. Trees were planted at 1.5 × 1.5 m spacing and irrigated by surface drip irrigation. Diameter at breast height (DBH) and tree height were recorded annually (2003–2006); wood volumes (WVol) and total aboveground biomass (TAB) were calculated from these measurements. Of the 25 clones tested, 19 were common to both sites. Mean height was greater at the Ontario site through the first 3 years (2003–2005). By the end of four seasons, the tallest Farmington entry was OP-367 at 9.4 m with 177 Mg ha⁻¹ TAB while the tallest Ontario entry was Malheur-3 at 8.9 m with 195 Mg ha⁻¹ TAB and several other clones had statistically similar production. Given the growth and productivity range at these two sites, it is difficult to make generalizations across wide areas, but it appears feasible to identify clones suited to alkaline soils in arid and semi-arid regions.     

Positive nitrogen balance of <Emphasis Type="Italic">Acacia mangium</Emphasis> woodlots as fallows in the Philippines based on <Superscript>15</Superscript>N natural abundance data of N<Subscript>2</Subscript> fixation

Nitrogen inputs from biological nitrogen fixation contribute to productivity and sustainability of agroforestry systems but they need to be able to offset export of N when trees are harvested. This study assessed magnitudes of biological nitrogen fixation (natural ¹⁵N abundance) and N balance of Acacia mangium woodlots grown in farmer’s fields, and determined if N₂ fixation capacity was affected by tree age. Tree biomass, standing litter, understory vegetation and soil samplings were conducted in 15 farmer’s fields growing A. mangium as a form of sequential agroforestry in Claveria, Misamis Oriental, Philippines. The trees corresponded to ages of 4, 6, 8, 10 and 12 years, and were replicated three times. Samples from different plant parts and soils (0–100 cm) were collected and analyzed for δ¹⁵N and nutrients. The B-value, needed as a reference of isotopic discrimination when fully reliant on atmospheric N, was generated by growing A. mangium in an N₂-free sand culture in the glasshouse. Isotopic discrimination occurring during N₂ fixation and metabolic processes indicated variation of δ¹⁵N values in the order of nodules > old leaves > young leaves > stems > litterfall and roots of the trees grown in the field, with values ranging from −0.8 to 3.5‰ except nodules which were enriched and significantly different from other plant parts (P < 0.0001). Isotopic discrimination was not affected by tree age (P > 0.05). Plants grown in N free sand culture exhibited the same pattern of isotopic discrimination as plants grown in the field. The estimated B-value for the whole plant of A. mangium was −0.86‰. Mature tree stands of 12 years accumulated up to 1994 kg N ha⁻¹ in aboveground biomass. Average proportion of N derived from N₂ fixation of A. mangium was 54% (±22) and was not affected by age (P > 0.05). Average yearly quantities of N₂ fixed were 128 kg N ha⁻¹ in above-ground biomass amounting to 1208 kg N fixed ha⁻¹ over 12 years. Harvest of 12-year old trees removed approximately 91% of standing aboveground biomass from the site as timber and fuel wood. The resulting net N balance was +151 kg N ha⁻¹ derived from remaining leaves, twigs, standing litter, and +562 kg N ha⁻¹ when tree roots were included in the calculation. The fast growing A. mangium appears to be a viable fallow option for managing N in these systems. However, other nutrients have to be replaced by using part of the timber and fuel wood sales to compensate for large amounts of nutrient removed in order for the system to be sustainable.     

Possibility of improvement in fundamental properties of wood of acacia hybrids by artificial hybridization

Growth, specific gravity, and wood fiber length of Acacia mangium, Acacia auriculiformis, artificial acacia hybrid clones, and combinations, which were planted in a trial forest in Bavi, Vietnam, in July 2001, were examined. The radial variations from pith to bark were investigated to clarify the effect of genetic factors on these traits. Superiority of hybrids over their parents ranged from 36.3% to 41.6% for diameter, from 20.0% to 25.3% for height, from 6.9% to 20.7% for specific gravity, and from 6.1% to 12.8% for wood fiber length. The hybrid possessed heterosis in diameter, height, specific gravity, and wood fiber length regardless of whether the female parent was A. mangium or A. auriculiformis. The profiles of wood fiber length and specific gravity in the radial direction were similar for all the trees investigated. Wood fiber length was initially 0.5–0.6 mm near the pith and then increased slowly, finally reaching 1.0–1.2 mm near the bark. The specific gravity of acacia increased from 0.49–0.58 near the pith to 0.63–0.74 near the bark. From a relative distance of 30% from the pith, the specific gravity increased slightly and seemed to be stable. The relations among tree diameter, specific gravity, and wood fiber length were fair and could be represented by positive linear regression formulas. Hybrids for which A. auriculiformis was the female parent and A. mangium was the male parent had a faster growth rate and longer wood fibers than the inverse hybrids. Part of this report was presented at the 6th Pacific Regional Wood Anatomy Conference, Kyoto, Japan, December 2005     

Screening for host responses in Acacia to a canker and wilt pathogen,Ceratocystis manginecans

In Vietnam, the productivity of Acacia hybrid (Acacia mangium x A. auriculiformis) plantations is being threatened by an aggressive canker pathogen, Ceratocystis manginecans, and selection for tolerance is the main control strategy. A pot trial was established in Binh Duong province to screen for the host response of nine Acacia genotypes (six Acacia hybrid clones, two A. auriculiformis clones and mixed provenance seedlings of A. mangium) to artificial inoculation with three isolates of C. manginecans. Lesion lengths as measured on the inner bark suggested that the two A. auriculiformis clones were relatively more tolerant to C. manginecans than the A. mangium genotype. In contrast, the lesion lengths of all six Acacia hybrid clones fell between the A. auriculiformis and A. mangium genotypes. The results of this study indicate that among the Acacia hybrid clones, BV10 showed the most tolerance to C. manginecans. Chemical analysis of crude sapwood extracts sampled from the lesion provided some evidence that induced phenolic compounds, particularly tetrahydroxyflavanone and condensed tannins may have a defensive role in the Acacia—C. manginecans pathosystem. However, results were not consistent across individual Acacia hybrid clones and A. mangium genotypes.     

Mixed-species plantations of Acacia mangium and Eucalyptus grandis in Brazil: 2: Nitrogen accumulation in the stands and biological N2 fixation

The sustainability of plantation forests is closely dependent on soil nitrogen availability in short-rotation forests established on low-fertility soils. Planting an understorey of nitrogen-fixing trees might be an attractive option for maintaining the N fertility of soils. The development of mono-specific stands of Acacia mangium (100A:0E) and Eucalyptus grandis (0A:100E) was compared with mixed-species plantations, where A. mangium was planted in a mixture at a density of 50% of that of E. grandis (50A:100E). N₂ fixation by A. mangium was quantified in 100A:0E and 50A:100E at age 18 and 30 months by the ¹⁵N natural abundance method and in 50A:100E at age 30 months by the ¹⁵N dilution method. The consistency of results obtained by isotopic methods was checked against observations of nodulation, Specific Acetylene Reduction Activity (SARA), as well as the dynamics of N accumulation within both species. The different tree components (leaves, branches, stems, stumps, coarse roots, medium-sized roots and fine roots) were sampled on 5–10 trees per species for each age. Litter fall was assessed up to 30 months after planting and used to estimate fine root mortality. Higher N concentrations in A. mangium tree components than in E. grandis might be a result of N₂ fixation. However, no evidence of N transfer from A. mangium to E. grandis was found. SARA values were not significantly different in 100A:0E and 50A:100E but the biomass of nodules was 20–30 times higher in 100A:0E than in 50A:100E. At age 18 months, higher δ¹⁵N values found in A. mangium tree components than in E. grandis components prevented reliable estimations of the percentage of N derived from atmospheric fixation (%Ndfa). At age 30 months, %Ndfa estimated by natural abundance and by ¹⁵N dilution amounted to 10–20 and 60%, respectively. The amount of N derived from N₂ fixation in the standing biomass was estimated at 62 kg N ha⁻¹ in 100A:0E and 3 kg N ha⁻¹ in 50A:100E by the ¹⁵N natural abundance method, and 16 kg N ha⁻¹ in 50A:100E by the ¹⁵N dilution method. The total amount of atmospheric N₂ fixed since planting (including fine root mortality and litter fall) was estimated at 66 kg N ha⁻¹ in 100A:0E and 7 kg N ha⁻¹ in 50A:100E by the ¹⁵N natural abundance method, and 31 kg N ha⁻¹ in 50A:100E by the ¹⁵N dilution method. The most reliable estimation of N₂ fixation was likely to be achieved using the ¹⁵N dilution method and sampling the whole plant.     

On-farm evaluation of two fast growing trees for biomass production for industrial use in Andhra Pradesh,Southern India

On-farm experiments were conducted in Khammam district of Andhra Pradesh from 2001 to 2006 to evaluate the biomass productivity, intercrop yields and profitability of Eucalyptus tereticornis clonal and Leucaena leucocephala variety K-636 based systems. Trees were planted at a spacing of 3 × 2 m and evaluated at three locations. Height growth was significantly higher in leucaena during the 4 year where as difference in diameter growth was not significant. Biomass partitioning to the bole was high in case of leucaena, ranged from 83% in 2.5–5 cm diameter at breast height (DBH) trees to 89% in 12.5–15 cm DBH trees and in eucalyptus clones the corresponding values were 71% in 2.5–5 cm DBH trees and 83% in 12.5–15 cm DBH trees. Marketable biomass productivity was higher with leucaena (95 Mg ha⁻¹) in comparison to eucalyptus (87 Mg ha⁻¹). Competition effects of trees on intercrops were observed from the 2 year (2002 post-rainy season). Intercrop yields were 45% of the sole crop in eucalyptus system and 36% in leucaena system during the 2 year. Sole eucalyptus and leucaena plantations and intercropping systems recorded higher gross and net returns over arable cropping. Therefore, it can be concluded that leucaena variety K636 and eucalyptus clonal based agroforestry systems are profitable alternatives to arable cropping under rainfed conditions.     

Phosphorus supply and cycling at long-term forest monitoring sites in Germany

In this study, the supply and input–output balances of phosphorus (P) were investigated for a 10-year-period at 85 long-term monitoring sites in German forest ecosystems under the European Level II programme. These sites encompass 23 European beech (Fagus sylvatica L.) stands, 9 oak stands comprised of common oak (Quercus robur L.) and/or sessile oak (Quercus petraea Liebl.), 20 Scots pine (Pinus sylvestris L.) and 33 Norway spruce (Picea abies H.Karst.) stands. We quantified P concentrations in needles and leaves, P inputs from the atmosphere, P outputs through leaching and harvesting, and total P in the soil and humus layers. The P concentrations in European beech leaves from two sites (>1 mg P g⁻¹ dry weight), and in Norway spruce needles from four sites (>1.2 mg P g⁻¹ dry weight), were deficient over several years. In contrast, the oak and Scots pine sites were well supplied with P. When P removal through harvesting was disregarded, P balances were positive or stable (median 0.21 kg P ha⁻¹ a⁻¹). With harvesting, balances were mostly negative (median −0.35 kg P ha⁻¹ a⁻¹), with long-term P removal from the forest ecosystems.     

Variation in wood properties of six natural acacia hybrid clones in northern Vietnam

Wood properties of six 8-year-old natural acacia hybrid clones between Acacia mangium and Acacia auriculiformis, planted in Bavi, Vietnam, were studied. The hybrid clones possessed obvious heterosis in growth and in some wood properties. The characteristics of growth, air-dry specific gravity, lengths of fibers and vessel elements, S₂ microfibril angle, green moisture content, and shrinkage were examined to clarify the variation among clones. From the results, the differences among the clones in growth and in some wood properties were significant. The pattern of distribution of specific gravity showed that there were low and high specific gravity zones in the stem. Specific gravity at stump height or at 3.0 m was useful for prediction of specific gravity in the whole tree stem. Moreover, clones with high specific gravity can be predicted at a young age. There was no significant correlation between diameter growth and specific gravity. Of the six clones studied, clone BV5 was selected as the best based on its growth ability and specific gravity. Part of this report was presented at the 57th Annual Meeting of the Japan Wood Research Society, Hiroshima, August 2007     

Does exceeding the critical loads for nitrogen alter nitrate leaching,the nutrient status of trees and their crown condition at Swiss Long-term Forest Ecosystem Research (LWF) sites?

Nitrogen (N) deposition exceeds the critical loads for this element in most parts of Switzerland apart from the Alps. At 17 sites (8 broadleaved stands, 8 coniferous stands, and 1 mixed stand) of the Swiss Long-term Forest Ecosystem Research network, we are investigating whether N deposition is associated with the N status of the forest ecosystems. N deposition, assessed from throughfall measurements, was related to the following indicators: (1) nitrate leaching below the rooting zone (measured on a subset of 9 sites); (2) the N nutrition of the forest stand based on foliar analyses (16 sites); and (3) crown defoliation, a non specific indicator of tree vitality (all 17 sites). Nitrate leaching ranging from about 2 to 16 kg N ha⁻¹ a⁻¹ was observed at sites subjected to moderate to high total N deposition (>10 kg ha⁻¹ a⁻¹). The C/N ratio of the soil organic layer, or, when it was not present, of the upper 5 cm of the mineral soil, together with the pool of organic carbon in the soil, played a critical role, as previous studies have also found. In addition, the humus type may need to be considered as well. For instance, little nitrate leaching (<2 kg N ha⁻¹ a⁻¹) was recorded at the Novaggio site, which is subjected to high total N deposition (>30 kg ha⁻¹ a⁻¹) but characterized by a C/N ratio of 24, large organic C stocks, and a moder humus type. Foliar N concentrations correlated with N deposition in both broadleaved and coniferous stands. In half of the coniferous stands, foliar N concentrations were in the deficiency range. Crown defoliation tended to be negatively correlated with N concentrations in the needles. In the majority of the broadleaved stands, foliar N concentrations were in the optimum nutritional range or, on one beech plot with high total N deposition (>25 kg ha⁻¹ a⁻¹), above the optimum values. There was no correlation between the crown defoliation of broadleaved trees and foliar concentrations.     

Phosphorus uptake and maize response to organic and inorganic fertilizer inputs in Rubona,Southern Province of Rwanda

Green manure of multipurpose trees is known to be a good source of nutrients to crop. However, most agroforestry species do not have adequate phosphorus (P) in their leaves. Supplementing green manure with moderate dose of P is a beneficial strategy to improve food security in Rwanda. This study examines the effects of Calliandra calothyrsus Meissner, Tithonia diversifolia Hensley A.Gray and Tephrosia vogelii Hook.f. green manure applied independently or in combination with triple super phosphate (TSP) and lime on maize yield and P uptake in the Oxic Tropudalf of Rubona, Rwanda. The treatments were the control, lime at 2.5 t ha⁻¹, TSP at 25 and 50 kg P ha⁻¹, leaf of C. calothyrsus, T. diversifolia, and T. vogelii each at 25 and 50 kg P ha⁻¹, respectively. Leaf shrubs biomass, TSP and lime were applied for four consecutive seasons (2001–2004). The results showed that the combination of green manure with TSP at a rate of 50 kg P ha⁻¹ significantly increased maize yield from 24 to 508% when compared to the control and T. divesifolia combined with TSP was leading (508%). Equally, the same treatments as indicated above showed higher P uptake (15.6–18. 6 kg P ha⁻¹) than the control (5 kg P ha⁻¹) and 65% of maize yields variation was explained by total P uptake. The plant residues quality such as C:N ratio, total plant N, and P significantly influenced the variability of maize grain yields.     

Efficiency of the indirect selection and the evaluation of the genotype by environment interaction using Pilodyn for the genetic improvement of wood density in <Emphasis Type="Italic">Cryptomeria japonica</Emphasis>

The efficiency of the indirect selection for wood density using the Pilodyn in Cryptomeria japonica was studied by comparing the Pilodyn penetration (PP) depth and the direct measurement of wood density in three test sites. The influence of the genotype by environment (G × E) interaction of wood density was estimated using the Pilodyn with common 12 C. japonica clones in 10 test sites in Kanto breeding region in Japan. The PP depth was highly correlated with wood density, and the genetic correlation between them was −0.88. The indirect selection using the Pilodyn realized 87% of the genetic gain obtained by the direct selection of wood density. The G × E interaction in PP depth was small. The ratio of the variance component of the G × E interaction to that of genotype was only 0.096 in the PP depth, whereas it was 0.700 in tree height and 1.410 in diameter at breast height. These findings indicate that the Pilodyn is useful for the genetic improvement of wood density in Cryptomeria japonica. The small G × E interaction in wood density estimated using the Pilodyn indicates that the relative clonal performance in wood density is stable among diverse environments in Kanto breeding region in Japan.     

Root activity of young <Emphasis Type="Italic">Acacia mangium</Emphasis> Willd trees: influence of stand density and pruning as studied by <Superscript>32</Superscript>P soil injection technique

Initial spacing and pruning are silvicultural strategies that influence the resource acquisition capabilities of trees. A field study was conducted in the humid tropics of peninsular India to test the assumptions that: (1) high stand density of Acacia mangium induces greater root uptake capacity close to the stem and from the subsoil; and (2) crown pruning stimulates greater root uptake capacity at proximal points. Root activity pattern of two-year-old A. mangium was evaluated as a function of three population densities (1,250, 2,500 and 5,000 stems ha⁻¹), with, and without 50% crown pruning, using ³²P soil injection. The label was placed at 25, 50 and 75 cm lateral distances and at 30 and 60 cm depth. Low density stands (1,250 stems ha⁻¹) generally showed higher ³²P recovery (P < 0.01), which was exaggerated by pruning. Pruned low density stands had 34% root activity at 25 cm, as against 23% for unpruned. The low density stands also showed higher root activity at 75 cm, signifying greater root spread. We suggest that high stem densities favour restricted spread of absorbing roots and may facilitate competitive downward displacement of roots. Pruning the lateral shoots at low stem densities may simulate this to some extent. The net outcome of interactions, however, will depend on trade-offs between stem density and tree management over time.     

Genetic control of fiber properties and growth in triploid hybrid clones of Populus tomentosa

To better understand the genetic control of fiber properties (fiber length [FL], fiber width [FW] and coarseness [C]) and growth traits (tree height [H], diameter at breast height [DBH] and stem volume [SV]) in triploid hybrid clones of Populus tomentosa carr., genetic relationships among selected fiber properties with growth traits were examined in five-year-old clonal field trials located in Yanzhou, Gaotang and Xiangfen, China. In total, 180 trees from 10 clones were sampled from the three sites. The site had a moderate effect on FW, C and tree growth, and a highly significant (P<0.001) effect on FL and fiber length/width (FL/W). Clonal effects were also significant (P<0.05) for all studied traits except for the DBH and SV. Clone×site interactions were significant for all studied traits (except for FL). The estimated repeatability of clonal mean for FL (0.91) was higher than for FW (0.88), C (0.77), FL/W (0.74), H (0.62), DBH (0.61) and SV (0.55). Intersite genetic correlation estimates indicated that fiber properties were more stable than growth traits. Positively insignificant genetic correlation estimates between FL and growth trait and negatively insignificant genetic correlation estimates between C and growth traits were observed. This suggests that in the triploid hybrid poplar, clones selection for growth traits will not result in a significant increase or reduction in the fiber properties.     

Reduced soil nutrient leaching following the establishment of tree-based intercropping systems in eastern Canada

Tree-based intercropping (TBI) systems, combining agricultural alley crops with rows of hardwood trees, are largely absent in Canada. We tested the hypothesis that the roots of 5–8 years old hybrid poplars, growing in two TBI systems in southern Québec, would play a “safety-net” role of capturing nutrients leaching below the rooting zone of alley crops. TBI research plots at each site were trenched to a depth of 1 m on each side of an alley. Control plots were left with tree roots intact. In each treatment at each site, leachate at 70 cm soil depth was repeatedly sampled over two growing seasons using porous cup tension lysimeters, and analyzed for nutrient concentrations. Daily water percolation rates were estimated with the forest hydrology model ForHyM. Average nutrient concentrations for all days between consecutive sampling dates were multiplied by water percolation rates, yielding daily nutrient leaching loss estimates for each sampling step. We estimated that tree roots in the TBI system established on clay loam soil decreased subsoil NO₃ ⁻ leaching by 227 kg N ha⁻¹ and 30 kg N ha⁻¹ over two consecutive years, and decreased dissolved organic N (DON) leaching by 156 kg N ha⁻¹ year⁻¹ in the second year of the study. NH₄ ⁺ leaching losses at the same site were higher when roots were present, but were 1–2 orders of magnitude lower than NO₃ ⁻ or DON leaching. At the sandy textured site, the safety net role of poplar roots with respect to N leaching was not as effective, perhaps because N leaching rates exceeded root N uptake by a wider margin than at the clay loam site. At the sandy textured site, significant and substantial reductions of sodium leaching were observed where tree roots were present. At both sites, tree roots reduced DON concentrations and the ratio of DON to inorganic N, perhaps by promoting microbial acquisition of DON through rhizodeposition. This study demonstrated a potential safety-net role by poplar roots in 5–8 year-old TBI systems in cold temperate regions.     

Nitrate-N dynamics following improved fallows and maize root development in a Zimbabwean sandy clay loam

Improved or planted fallows using fast-growing leguminous trees are capable of accumulating large amounts of N through biological N₂-fixation and subsoil N capture. During the fallow phase, the cycling of nutrients is largely efficient. However, there are few estimates of the fate of added N during the cropping phase, after the 'safety net' of fallow-tree roots is removed. Nitrate-N at the end of the fallow phase, which is pre-season to the subsequent crop, was monitored in seven land use systems in successive 20-cm soil layers to 120 cm depth at Domboshawa, Zimbabwe in October 2000. Thereafter, nitrate-N dynamics was monitored during cropping phase until April 2001 at 2-week intervals in plots that had previously 2-year planted fallows of Acacia angustissima and Sesbania sesban, and in a continuous maize control. Pre-season nitrate concentrations below 60 cm soil depth were <3 kg N ha⁻¹ layer⁻¹ for S. sesban, A. angustissima, Cajanus cajan and natural woodland compared with the maize (Zea mays L.) control, which had >10 kg N ha⁻¹ layer⁻¹. There was a flush of nitrate in the S. sesbania and A. angustissima plots with the first rains. Topsoil nitrate had increased to >29 kg N ha⁻¹ by the time of establishing the maize crop. This increase in nitrate in the topsoil was not sustained as concentrations decreased rapidly due to leaching. Nitrate then accumulated below 40 cm, early in the season when maize root length density was still low (<0.1 cm cm⁻³) and inadequate to effectively intercept the nitrate. It is concluded that under light soil and high rainfall conditions, there is an inherent problem in managing nitrate originating from mineralization of organic materials as it accumulates at the beginning of the season, well ahead of peak demand by crops, and is susceptible to leaching before the crop root system develops. This revised version was published online in June 2006 with corrections to the Cover Date.     

Precipitation chemistry at a high elevation forest in central Taiwan

High elevation ecosystems are particularly sensitive to environmental change. Mountain agriculture is extending to areas at high elevations in Taiwan but the effects on nutrient cycling of the surrounding ecosystems are largely unknown. We examined precipitation chemistry at Piluchi Experimental Forest in central Taiwan to evaluate the contributions of local air pollution and long-range transport of air pollutants on nutrient cycling at this seemingly remote forest. Sea-salt aerosols and anthropogenic pollutants resulting from long-range transport of air pollutants and mountain agriculture activities are the key factors affecting precipitation chemistry at Piluchi Experimental Forest. Precipitation chemistry was dominated by ions of oceanic origin in the summer and by anthropogenic pollutants SO₄ ²⁻, NO₃ ⁻ and NH₄ ⁺ in the winter and spring, the northeast monsoon season. The much higher concentrations of S and N in the northeast monsoon season than the summer suggest a substantial contribution from long-range transport as the prevailing air masses moved from inland China and passed over the industrialized east coast of China before arriving in Taiwan. The very high concentration of NH₄ ⁺ (22 μeq L⁻¹) in the spring, when the local application of N-containing fertilizers was high, signifies the influences of mountain agriculture. Despite very low concentrations relative to other sites in Taiwan, annual input of NH₄ ⁺ (3.6 kg ha⁻¹ year⁻¹), NO₃ ⁻ (7.2 kg ha⁻¹ year⁻¹) and SO₄ ²⁻ (10 kg ha⁻¹ year⁻¹) via precipitation was substantial suggesting that high elevation ecosystems of Taiwan are not free from the threat of atmospheric deposition of pollutants.     

Effect of pruning frequency and pruning height on the biomass production of <Emphasis Type="Italic">Tithonia diversifolia</Emphasis> (Hemsl) A. Gray

Addition of tree or shrub prunings through alley cropping or biomass transfer systems have contributed to sustainable land-use systems in the tropics. Long term productivity of biomass transfer systems require shrub or tree species that coppice after cutting to provide sufficient plant nutrients. The effect of pruning frequency and cutting height on the biomass production of Tithonia diversifolia was studied to provide information for managing hedges. Results showed that height of cutting, pruning frequency, and their interactions significantly affected dry matter production of T. diversifolia. The results also showed that a significantly higher biomass production could be produced when Tithonia was pruned at long time intervals. Pruning height was also of importance in the harvesting of Tithonia biomass and it was evident that dry matter production was highest when Tithonia was pruned bimonthly at 50 cm height. With bi-monthly pruning frequency, dry matter production could be as high as 7.2 t ha⁻¹ yr⁻¹ which might be a sufficient biomass to improve soil productivity in biomass transfer systems.     

Effect of residue management and fertiliser application on the productivity of a Eucalyptus hybrid and Acacia mangium planted on sloping terrain in northern Vietnam

Forest plantation growers in Vietnam commonly burn residues after harvesting and often apply suboptimal amounts of nutrients during plantation establishment. We examined whether the retention of forest residue, and application of phosphorus fertiliser at higher rates, can increase rates of growth. A factorial combination of residue management (burning vs retention) and phosphorus fertiliser application at planting (15 vs 100 kg ha^?1) treatments were applied at a steeply sloping site in northern Vietnam. Two adjacent experiments were established, one with Acacia mangium and the other with a Eucalyptus hybrid (Eucalyptus urophylla × Eucalyptus pellita). Standing volume and leaf area index in A. mangium were greater following burning; this was mostly attributable to the significantly higher survival rate of seedlings. Burning of residues was associated with increases in the number of large branches per tree, and a higher crown damage index (CDI). In the Eucalyptus hybrid, diameter and height responses to the higher rate of fertiliser were observed at age 6 and 12 months, but not beyond. High phosphorus application also led to higher CDI. Standard fertiliser treatment, applied in amounts equivalent to 17, 15 and 8 kg ha^?1 of nitrogen, phosphorus and potassium, respectively, was adequate to meet the early growth requirement of eucalypt and acacia plantations at this site. The relatively low amounts of harvest residue and high fertility levels at the site may have masked more significant responses of trees to the silvicultural treatments applied in this study. On steep slopes, especially if soil is poorly fertile, harvest residue retention with adequate weed and termite control may be preferential to burning as it is closely correlated with reducing factors that negatively impact productivity, i.e. water run-off and soil erosion.     

Partition of nocturnal sap flow in Acacia mangium and its implication for estimating the whole-tree transpiration

We analyzed the partition of nocturnal sap flow into refilling of internal water storage and transpiration in Acacia mangium. Sap flow of trees was monitored continuously with Granier’s sensors for estimating the whole-tree transpiration. Possible night transpiration and stomatal conductance at the leaf level in the canopy were measured with a LI-6400 photosynthesis measuring system. For nocturnal leaf transpiration and stomatal conductance were weak, nocturnal sap flow of mature A. mangium trees was mainly associated with water recharge in the trunk. No significant change in night water recharge of the trunk was found at both seasonal and inter-annual scales. Morphological features of trees including diameter at the breast height (DBH), tree height, and canopy size could explain variances of night water recharge. Furthermore, although the contribution of nocturnal sap flow to the total transpiration varied among seasons and DBH classes, the error caused by night water recharge on wholetree transpiration was negligible. __________ Translated from Journal of Plant Ecology (Chinese Version), 2007, 31 (5): 777–786 [译自: 植物生态学报]     

Relationship of wood composition to growth traits of selected open-pollinated families of <Emphasis Type="Italic">Eucalyptus urophylla</Emphasis> from a progeny trial in Vietnam

Lignin and cellulose contents and wood basic density were related to diameter at breast height (DBH) in six fast-growing and five slow-growing families from a combined progeny test and seedling seed orchard of Eucalyptus urophylla grown for 10 years in northern Vietnam. The mean cellulose content of the fast-growing families was significantly higher than that of the slow growing-families (40.0 and 37.1%, respectively), and for individual trees cellulose content was significantly correlated phenotypically with DBH. Wood basic density was significantly lower in the fast-growing group than in the slow-growing group (0.506 and 0.535 g cm⁻³, respectively), and was significantly negatively correlated phenotypically with DBH. The lignin contents were not significantly different between groups. Cellulose content and wood basic density were not correlated. The main conclusion is that there is no obstacle to combining high growth rate with high cellulose content, for plantation of forests intended mainly for pulpwood.